Adventitious roots are key to the development of nebkhas in extremely arid regions

Abstract

Nebkhas, discrete sand mounds formed with a plant, are a common landscape feature critical to the stability of desert ecosystems. However, adaptations which allow plants to thrive in nebkhas in extremely arid regions are still unclear. The objectives of this study were to test the role of adventitious roots (AR) in the growth and development of Nitraria sphaerocarpa-vegetated nebkhas. We determined biomass distribution patterns and nutrient levels in small, medium, and large nebkhas representing different stages of nebkha development from young to mature, respectively. Our results showed that biomass allocation patterns and nutrient levels were very different among the different nebkha sizes. The proportions of leaves and stems increased with the increase in nebkha size, while those of AR and initial roots (IR) decreased. This indicated that, with an increase in nebkha size, N. sphaerocarpa allocated a higher proportion of biomass to leaves and stems mainly at the expense of roots, and that allowed plants to withstand increased burial depth. The proportion of AR, especially fine AR, varied among nebkha sizes. The proportion of AR in large nebkhas was significantly higher than in small nebkhas. For small and medium nebkhas, the proportion of fine AR was smaller than that of fine IR; for large nebkhas, the proportion of fine AR was higher. This indicated that AR, produced higher on the buried stems in the late stages of nebkha development, may provide increased access to water and nutrients to ensure nebkha survival. Nutrient levels were different in AR and IR of different nebkha growth stages. N and P contents of coarse AR and IR increased with nebkha size. For small nebkhas, N and K levels in fine AR were significantly lower than those in IR; however, for large nebkhas, N and K levels in AR were significantly higher than those in IR. This indicated that AR in the late stages of nebkha development may have stronger absorptive capacity for resources than IR. We conclude that AR are key factor which ensured both the survival and development of N. sphaerocarpa nebkha in extremely arid environment.